/**
 * Base64 转 Blob
 * @param {String} dataurl    base64内容
 * @param {String} mimetype   mime标识
 * @return {Blob} blob
 */
export function dataURLToBlob(dataurl, mimetype) {
    let arr = dataurl.split(','),
        mime = mimetype || arr[0].match(/:(.*?);/)[1],
        bstr = atob(arr[1]),
        n = bstr.length,
        u8arr = new Uint8Array(n);

    while (n--) {
        u8arr[n] = bstr.charCodeAt(n);
    }
    return new Blob([u8arr], { type: mime });
}

/**
 * Blob 转 Base64
 * @param {Blob} blob    Blob对象
 * @return {Object} promise
 */
export function blobToDataURL(blob) {
    return new Promise((resolve, reject) => {
        let fileReader = new FileReader();

        fileReader.onload = (e) => {
            resolve(e.target.result);
        }
        fileReader.readAsDataURL(blob);
    });
}

/**
 * Base64 转 File
 * @param {String} dataurl    base64内容
 * @param {String} filename   文件名
 * @return {File} file
 */
export function dataURLtoFile(dataurl, filename) { //将base64转换为文件
    let arr = dataurl.split(','),
        mime = arr[0].match(/:(.*?);/)[1],
        bstr = atob(arr[1]),
        n = bstr.length,
        u8arr = new Uint8Array(n);

    while (n--) {
        u8arr[n] = bstr.charCodeAt(n);
    }
    return new File([u8arr], filename, { type: mime });
}
/**
 * Blob 转 Base64
 * @param {Blob} blob    Blob对象
*/
export function blobToUrl(blob) {
    return window.URL.createObjectURL(blob)
}
